A common method for the manufacture of asphalt shingles is the production of a continuous sheet of asphalt material followed by a shingle cutting operation which cuts the material into individual shingles. In the production of asphalt sheet material, either a glass fiber mat or an organic felt mat is passed through a coater containing hot liquid asphalt to form a tacky, asphalt coated sheet. Subsequently, the hot asphalt coated sheet is passed beneath one or more granule applicators which discharge protective surface granules onto portions of the asphalt sheet material.
In the manufacture of colored shingles, two types of granules are typically employed. Headlap granules are granules of relatively low cost used for the portion of the shingle which will be covered up on the roof. Colored granules or prime granules are of relatively higher cost and are applied to the portion of the shingle which will be exposed on the roof.
To provide a color pattern of pleasing appearance, the colored portion of the shingles may be provided with areas of different colors. Usually the shingles have a background color and a series of granule deposits of different colors or different shades of the background color. The term "blend drop", as used herein, refers to the flow of granules of different colors or different shades of color that are discharged from a granule applicator toward the asphalt coated sheet. The term "granule deposit", as used herein, refers to the blend drop of granules after it has been deposited on the sheet.
A common method for manufacturing the shingles is to discharge blend drops onto spaced areas of the tacky, asphalt coated sheet. Background granules are then discharged onto the sheet and adhere to the tacky, asphalt coated areas of the sheet between the granule deposits formed by the blend drops.
One of the problems with typical granule application equipment is that it depends on mechanical movement to discharge blend drops onto the moving asphalt coated sheet. Usually the granules are fed from a hopper onto a fluted roll from which, upon rotation, the granules are discharged onto the sheet. The roll is ordinarily driven by a drive motor, and the roll is positioned in the drive or non-drive position by means of a brake-clutch mechanism. The requirement for mechanical action has inherent limitations which prevent a very precise beginning and ending to the blend drop. Also, once the mechanical action takes place, there is a short time lag as gravity takes effect on the granules and they drop onto the moving asphalt coated sheet. Consequently, there is a limit to the sharpness of the granule deposits on the shingle. As shingle manufacturing lines go up in speed, the lack of sharpness is accentuated and the distinction between the granule deposits and the background color becomes fuzzy. The lack of sharpness puts a severe limitation on the kinds of patterns and color contrasts which can be applied to shingles at high production speeds.
One method for manufacturing shingles having sharply defined granule deposits involves the application of the background color granules over the entire exposed tacky surfaces of the shingles. Adhesive such as hot asphalt is then applied in a pattern on top of the background color granules on the sheet, in the areas where the granule deposits are to be applied. Then the granule deposits are applied and adhere to the shingle only on the areas of adhesive. This method of applying granules is described in U.S. Pat. No. 4,352,837, issued Oct. 5, 1982 to Kopenhaver. Unfortunately, the application of the double layer of granules in the areas of granule deposits make these shingles relatively expensive, heavy and inflexible.
A recently developed improved method for discharging blend drops onto the moving asphalt coated sheet uses an apparatus known as a pneumatic blender. This apparatus employs a pneumatic gating mechanism to provide a relatively high degree of precision in discharging the blend drops. The flow of granules is started, stopped and controlled by providing pneumatic pressure changes in a buffer chamber positioned adjacent an accumulation of granules in a granule nozzle. When the pneumatic pressure is increased, the flow of granules is ejected under pressure onto the moving asphalt coated sheet instead of dropping solely by gravity. These features of the pneumatic blender allow more sharply defined granule deposits to be formed on the moving asphalt coated sheet. A preferred pneumatic blender is disclosed in U.S. Pat. No. 5,520,889, issued May 28, 1996 to Burton et al. (incorporated by reference herein).
Other improvements have also been made in methods of applying granule deposits. For example, U.S. Pat. No. 5,405,647, issued Apr. 11, 1995 to Grubka et al., discloses a method for applying granules to a moving asphalt coated sheet to form areas having sharp leading and trailing edges. However, it would still be desirable to provide a method for making a variety of unique and attractive patterns of granule deposits on asphalt coated sheets. Granule deposits applied by typical methods are usually formed of a single color or color blend of granules. Typical granule deposits also come in a limited variety of shapes. Thus, it would be desirable to provide a method and apparatus for forming granule deposits from two or more separate colors of granules. It would also be desirable to provide a method and apparatus for forming granule deposits having unique shapes, and for allowing the shapes to be easily changed on different shingles. These advantages should be provided without the drawbacks of applying a double layer of granules on the shingles.